• Category
  • Length Range
    16.4-55.0 µm
  • Width Range
    6.2-10.1 µm
  • Striae in 10 µm



Valves are lanceolate and slightly heteropolar. Valve apices are obtuse and weakly protracted in some specimens, not protracted in others. The axial area is narrow and linear in smaller specimens, moderately wide and lanceolate in larger specimens. The central area is slightly asymmetric and transversely rectangular. It is bordered by one or two shortened striae on the primary side adjacent to the stigma, and one or two shorter striae on the secondary side of the valve. The raphe is lateral and somewhat sinuous. External proximal raphe ends are weakly expanded and slightly deflected toward the primary side. Terminal raphe ends are are sinuous and deflected toward the secondary side of the valve. Striae are parallel or slightly radiate at the valve center, and become more radiate toward the apices. Areolae in the striae number 28-34 in 10 µm. An initial valve was observed at 55 µm in length.

The relation between this taxon and G. angustatum var. obtusatum (Kützing) Grunow in Van Heurck, as reported from the eastern and central U.S. (Patrick & Reimer 1975), is in need of clarification.


Gomphonema americobtusatum was described from Canada. In the Northwest U.S. it is widely distributed in mountain waters, primarily in the Rockies and Cascades, but also on the east side of the Sierra Nevada Range (see map below). Abundance-weighted values for selected water quality variables (table below) suggest that it prefers cool, well-oxygenated, low nutrient and somewhat alkaline water of low conductivity.

Atlantic  Pond  Gnp 1
Credit: Loren Bahls
Atlantic Pond, Glacier National Park, Montana: home of Gomphonema americobtusatum.
Gomphonema Americobtusatum Map
Credit: Montana Diatom Database
Distribution of Gomphonema americobtusatum in the Northwest United States.
Gomphonema Americobtusatum Ecology
Credit: Montana Diatom Database
Abundance-weighted values of water quality variables for Gomphonema americobtusatum in the Northwest U.S.

Original Description

  • Author
    E.Reichardt and Lange-Bert. 1999
  • Length Range
    25-60 µm
  • Width
    8.6-10.7 µm
  • Striae in 10µm

Original Images

Gomphonema Americobtusatum Origimag001
Gomphonema Americobtusatum Origdesc001

Cite This Page

Bahls, L. (2017). Gomphonema americobtusatum. In Diatoms of North America. Retrieved July 22, 2018, from https://diatoms.org/species/gomphonema_americobtusatum


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Gomphonema americobtusatum from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.